Secure Electronic Mail System

1. A computer-implemented method of securely communicating e-mail messages, comprising at a client device: sending, to a server system, an e-mail message addressed to a recipient from a sender via a remote client executed on the client device; receiving, from the server system, a substitute message based on the e-mail message, the substitute message lacking at least some message content of the e-mail message, and including a link to a component that provides functionality for the recipient to securely retrieve the e-mail message from the server system; and sending the substitute message to the recipient, wherein the substitute message includes a message access key containing non-secret information which describes the e-mail message, the server system from which the e-mail message is to be retrieved, and a unique message ID that identifies the e-mail message on the server system.

2. The method of claim 1 , wherein the remote client comprises an e-mail client plug-in configured to run in conjunction with an e-mail client program on the client device.

3. The method of claim 1 , wherein the client communicates with the server system via an HTTPS connection over a computer network.

4. The method of claim 1 , wherein the substitute message is sent to the recipient via a SMTP server associated with an e-mail address of the sender.

5. The method of claim 1 , wherein the component that provides functionality for the recipient to securely retrieve the e-mail message from the server system comprises a link to a network location for downloading an e-mail client plug-in that is capable of securely retrieving and displaying the e-mail message.

6. The method of claim 1 , wherein the component that provides functionality for the recipient to securely retrieve the e-mail message from the server system comprises a link to a web-based interface that provides functionality for viewing the e-mail message.